Preparation and characterization of a novel organic–inorganic hybrid nanostructure: application in synthesis of spirocompounds

Article abstract of DOI:10.1007/s11164-020-04130-x

Abstract: Immobilization and heterogenization of acidic/basic groups or organic tags on inorganic supports have found many important applications in recent years. In this investigation, a new hybrid organic–inorganic nanostructure was prepared. The struct

Full text of DOI:10.1007/s11164-020-04130-x

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-020-04130-x
Preparation and characterization of a novel
organic–inorganic hybrid nanostructure: application
in synthesis of spirocompounds
Najmieh Ahadi · Mohammad Ali Bodaghifard1,2 · Akbar Mobinikhaledi1
1
Received: 15 December 2019 / Accepted: 16 March 2020
©
Springer Nature B.V. 2020
Abstract
Immobilization and heterogenization of acidic/basic groups or organic tags on inor-
ganic supports have found many important applications in recent years. In this inves-
tigation, a new hybrid organic–inorganic nanostructure was prepared. The structure
of novel nanomaterial was characterized by Fourier transform infrared spectroscopy,
X-ray diꢀraction, thermogravimetric analysis, vibrating sample magnetometer, scan-
ning electron microscopy and the energy-dispersive X-ray spectroscopy techniques.
The spirocompounds, especially spiroperimidines and pyranopyrazoles, are impor-
tant structures with diverse biological activities and many applications in industries.
So, the prepared hybrid nanomaterial was used as an eꢁcient catalyst in the one-pot,
green and simple protocol for the synthesis of pyranopyrazole, spiropyranopyrazole
and spiroperimidine derivatives. The structure of some compounds is characterized
1
13
by FT-IR, H-NMR and C-NMR analyses. In addition, the proposed intermediates
were synthesized and identiꢂed to prove the presented mechanism of the reaction.
This hybrid nanomaterial is a recyclable and highly eꢁcient heterogeneous catalyst
and easily separated by an external magnet from the reaction media. The short reac-
tion time, high eꢁciency, operational safety and use of environmentally benign sol-
vent are some beneꢂts of this procedure.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4
-020-04130-x) contains supplementary material, which is available to authorized users.
*
Mohammad Ali Bodaghifard
mbodaghi2007@yahoo.com; m-bodaghifard@araku.ac.ir
1
2
Department of Chemistry, Faculty of Science, Arak University, 38156-8-8349 Arāk, Iran
Institute of Nanosciences and Nanotechnology, Arak University, 38156-88349 Arāk, Iran
Vol.:(012
1
3456789)
3

N. Ahadi et al.
Graphic abstract
Keywords Nanostructures · Hybrid materials · Heterogeneous catalysis ·
Pyranopyrazole · Spirocompounds · Green chemistry
Introduction
Magnetic nanoparticles have found many applications in various ꢂelds such as drug
delivery, hyperthermia, magnetic resonance imaging (MRI), cell and stem cell sep-
aration, pharmacology, enzyme immobilization, magnetic ꢃuids, sensor, pigments
and catalysis area [1–4]. In recent years, magnetic nanoparticles have received
considerable attention as the catalysts in organic chemistry because of exceptional
properties including high surface area, thermal stability, low toxicity, strong activity,
easy separation (by a magnet), the capability of surface modiꢂcation, reusability and
recyclability in the organic reaction for several runs without noticeable loss of cata-
lytic activity [4–10]. The manganese ferrite (MnFe O ), as a class of soft magnetic
2
4
materials with distinct advantages like extraordinary saturation, low toxicity, excel-
lent compatibility and superparamagnetic properties, has obtained particular interest
[
11].
Multicomponent reactions (MCRs) have attracted considerable attention in medici-
nal chemistry and modern organic synthesis because of time, energy and environmen-
tal conservation [12]. MCRs produce complex and diverse combinations of products
and follow many principles of green chemistry, such as solvent-free or aqueous con-
dition, atom economy, energy saving with short reaction times, waste diminish, high
yields and selectivity [12–14]. Possible elimination of hazardous solvents and using
1
3

Preparation and characterization of a novel organic–inorganic…
solvent-free or aqueous conditions in MCRs have a notable impact on the protection of
the environment [12–14].
Among the various classes of heterocyclic compounds, perimidines and pyranopyra-
zoles are important structures with diverse biological activities [15–19]. Furthermore,
perimidine and pyranopyrazole derivatives have many applications in industries and
agriculture, such as organic solar cells, plasma display panels, optical recording media,
molecular switches, photochemical memory devices, insecticides, acaricides and her-
bicides [17, 20]. Spirocompounds with structural rigidity are bioactive materials like
antimicrobial, hypoglycemic, antifungal, anti-inꢃammatory, anti-bacterial and antican-
cer [16, 21–25]. Due to their broad range of pharmacological activity and industrial
applications, several methods have been reported for the synthesis of pyranopyrazole,
spiropyranopyrazoles, spiroperimidines and other spirocompounds [26–29]. However,
most of these methods experience limitations such as low yields, elevated temperatures,
prolonged reaction time and unrecyclable catalysts. As a result, the development of
green and straightforward methods for the synthesis of pyranopyrazole, spiropyrano-
pyrazoles and spiroperimidines is necessary.
The heterogenization of homogeneous acidic and basic groups in catalytic reactions
(
such as covalently bound acidic or basic catalysts) typically allows for the easy sepa-
ration and beneꢂcial reuse of catalysts. The inorganic-supported catalysts, especially
hybrid organic–inorganic magnetic nanomaterials, have been widely used in recent
years that could be extremely useful in the catalysis area [6]. Hence, herein, we intro-
duce a clean and eꢁcient synthetic way for the preparation of pyranopyrazole, spiro-
pyranopyrazoles and spiroperimidines gently using MNPs@SiO -BTEAT-SO H parti-
2
3
cles as a novel hybrid catalyst in mild and green conditions.
Results and discussion
Preparation of MNPs@SiO ‑BTEAT‑SO H catalyst
2
3
The schematic preparation of MNPs@SiO -BTEAT-SO H particles is shown in
2
3
Scheme 1. MnFe O nanoparticles were prepared using the co-precipitation method
2
4
[
30]. Subsequently MnFe O nanoparticles were coated with a silica layer via the
2 4
Stöber procedure [30, 31]. Then, 3-aminopropyltriethoxysilane (APTS) was bound
covalently to the OH groups on the MnFe O @SiO surface to gain MnFe O @SiO -
2
4
2
2
4
2
PrNH nanostructure. MnFe O @SiO -PrNH nanoparticles in the presence of Et N
2
2
4
2
2
3
as a base were reacted with cyanuric chloride. MnFe O @SiO -Pr-BTEAT particles
2
4
2
were prepared from the reaction between MnFe O @SiO -Pr-TDCl and triethanola-
2
4
2
2
mine. Ultimately, the reaction of MnFe O @SiO -Pr-BTEAT with chlorosulfonic acid
2
4
2
was performed, and the desired hybrid material (MNPs@SiO -BTEAT-SO H) was
2
3
obtained.
1
3

N. Ahadi et al.
Scheme 1 Preparation steps of MNPs@SiO -BTEAT-SO H as a new hybrid catalyst
2
3
Characterization of MNPs@SiO ‑BTEAT‑SO H catalyst
2
3
The FT‑IR spectroscopy
−
1
For all synthesized MNPs (Fig. 1), the characteristic band at 587 cm is prop-
erly assigned to the Fe–O bond stretching vibration. Also, the H–O–H twisting
−
1
−1
vibration appeared at 1627 cm . The absorption bands at 459 cm (rocking
−
1
−1
mode), 800 and 954 cm (bending), and 1087 cm (asymmetric stretching) are
related to Si–O–Si groups and conꢂrm the formation of SiO shell (Fig. 1b). The
2
−
1
weak bands at 2974 and 2930 cm are attributed to C–H stretching vibrations,
establishing the covalent bonding of organic tags. The spectra of MNPs-TDCl
2
−
1
and MNPs-BTEAT (Fig. 1d, e) show bands around 1450 to 1650 cm that are
typically corresponding to C=N, C=C, C–N and C–O bonds and conꢂrm the
−
1
heterocyclic ring attachment [27]. The appeared band around 700 cm at the
spectrum of MNPs-TDCl (Fig. 1d) is related to C–Cl stretching vibration. The
2
elimination of this band in the spectrum of MNPs-BTEAT (Fig. 1e) promptly
conꢂrms the successful substitution of Cl groups with triethanolamine. Even-
tually, MNPs@SiO -BTEAT-SO H was characterized by the absorption band
2
3
−
1
at 1201 cm , related to O=S=O moieties, that has overlapped with Si–O–Si
stretching band [32] (Fig. 1f).
1
3

Preparation and characterization of a novel organic–inorganic…
Fig. 1 A FT-IR spectra for a MnFe O , b MnFe O @SiO , c MnFe O @SiO -PrNH , d MnFe O @
2
4
2
4
2
2
4
2
2
2
4
SiO -Pr-TDCl , e MnFe O @SiO -Pr-BTEAT, f MNPs@SiO -BTEAT-SO H. B Expanded FT-IR spec-
2
2
2
4
2
2
3
tra for (d, e, f)
The XRD diꢀraction patterns
The XRD patterns for MnFe O (a) and MNPs@SiO -BTEAT-SO H (b) are shown
2
4
2
3
in Fig. 2. Diꢀraction peaks at 2θ=30, 35, 43, 53, 57 and 63 can be assigned to the
(
200), (311), (400), (331), (422) and (333) miller planes of MnFe O , respectively.
2
4
These data are granting to the standard MnFe O sample (JCPDS card no. 1964-
2
4
7
3) and instantly conꢂrm the cubic spinel structure for MnFe O nanoparticles. The
2
4
broad peak at 2θ=17–25 is related to the amorphous SiO shell on the surface of
2
MnFe O cores (Fig. 2b) [4]. The average size for MNPs@SiO -BTEAT-SO H is
2
4
2
3
calculated to be about 29 nm [25].
1
3

N. Ahadi et al.
Fig. 2 XRD patterns for MnFe O (a) and MNPs@SiO -BTEAT-SO H (b)
2
4
2
3
The TGA‑DTA and DTG analyses
The stability and functionalization of the MNPs@SiO -BTEAT-SO H catalyst were
2
3
evaluated by the TGA, DTG and DTA analyses (Fig. 3). TGA curve outlined three
steps of weight loss for the MNPs@SiO -BTEAT-SO H catalyst at 25–800 °C. The
2
3
ꢂrst step shows 3% weight loss at T<200 °C that is related to the removal of physi-
cally absorbed solvent and surface hydroxyl groups. The second step shows 12%
Fig. 3 TGA and DTG analysis for MNPs@SiO -BTEAT-SO H
2
3
1
3

Preparation and characterization of a novel organic–inorganic…
weight loss at 200–590 °C range, attributed to the decomposition of organic moi-
eties in the hybrid nanomaterial. The weight loss (11%) at T>600 °C shows the
destruction of the silica layer and particle deformation. This mass loss shows that
+
0
.13 mmol of H was loaded on 1 gr MNPs@SiO -BTEAT-SO H catalyst. These
2
3
results assure the stability of the MNPs@SiO -BTEAT-SO H particles at below
2
3
2
00 °C that is in agreement with back titration results and establish that the organic
groups are successfully loaded on the surface of MnFe O nanoparticles. DTG
2
4
analysis shows that MNPs@SiO -BTEAT-SO H nanoparticles were deformed at
2
3
5
80 °C. Moreover, the DTA diagram (blue curve) revealed that this gradual process
was endothermic.
Magnetic properties (VSM analysis)
The magnetization curve of MnFe O and MNPs@SiO -BTEAT-SO H is shown in
2
4
2
3
Fig. 4. The magnetization hysteresis loops for samples (a) and (b) are S-like and
show superparamagnetic properties for them. The saturation magnetization (Ms)
is 33 Oe for MnFe O (a) and 22 Oe for MNPs@SiO -BTEAT-SO H (b). Data
2
4
2
3
show that Ms for MNPs@SiO -BTEAT-SO H is lower than the MnFe O core.
2
3
2
4
These direct results can amply conꢂrm the successful preparation of MNPs@SiO -
2
BTEAT-SO H structure.
3
The SEM, EDS and EDS map scan analyses
The size and morphology of MNPs@SiO -BTEAT-SO H particles were considered
2
3
employing the FE-SEM analysis (Fig. 5a). The results show an average diameter of
2
0–35 nm and nearly spherical shape of nanoparticles that are in agreement with
the obtained results from XRD patterns. The energy-dispersive X-ray spectroscopy
(
EDS) result, obtained from FE-SEM analysis, is shown in Fig. 5b. This analysis
indicates clearly the presence of S, N, O, Si, Fe and Mn elements. The higher inten-
sity of the Si peak compared with Mn and Fe peaks indicates that the MnFe O
2
4
Fig. 4 VSM analysis for a MnFe O and b MNPs@SiO -BTEAT-SO H
2
4
2
3
1
3

N. Ahadi et al.
Fig. 5 FE-SEM (a), EDS (b) and column chart for quantitative results obtained from EDS (c) analyses
for MNPs@SiO -BTEAT-SO H
2
3
nanoparticles were coated by SiO shell. Also, besides the column chart for quan-
2
titative results obtained from EDS analysis is shown in Fig. 5c. Based on the col-
umn chart, W% for S/N is 0.70 that is in agreement with the proposed structure of
nanoparticles (S/N=0.66). EDS map scanning spectra in Fig. 6 show the disper-
sion–aggregation phenomenon of Si, O, C, N, S, Fe, Mn and integration of the outer
surface of MNPs@SiO -BTEAT-SO H particles. The diꢀerent color spots over the
2
3
dark background conꢂrm the location of the relative elements on the external sur-
face of MNPs@SiO -BTEAT-SO H particles. The blue, purple, red, white, orange,
2
3
golden, green and integration spots in Fig. 6 corresponded to carbon (C), iron (Fe),
manganese (Mn), nitrogen (N), sulfur (S), oxygen (O), silicon (Si) and integration,
respectively.
The catalytic activity of MNPs@SiO ‑BTEAT‑SO H
2
3
The catalytic activity of MNPs@SiO -BTEAT-SO H was carefully investigated
2
3
in the synthesis of spiroperimidines, pyranopyrazoles and spiropyranopyrazoles
(
Schemes 2, 3). Primitively, the catalytic activity of MNPs@SiO -BTEAT-
2
SO H was examined in the synthesis of spiroperimidine derivatives. The reac-
3
tion of cyclohexanone (1 mmol) and naphthalene-1,8-diamine (1 mmol) as a
1
3

Preparation and characterization of a novel organic–inorganic…
Fig. 6 EDS map analysis for MNPs@SiO -BTEAT-SO H
2
3
Scheme 2 Synthetic pathway of spiroperimidine derivatives
model reaction was performed in various conditions (Table 1). The results show
the most productive eꢁciency gained in the presence of 20 mg MNPs@SiO -
2
BTEAT-SO H as a catalyst and EtOH/H O as solvent at reꢃux condition (Table1,
3
2
Entry 6). Also, the presence of a catalyst is necessary for reaction performance
(
Table1, Entry 5). Finally, the model reaction was performed in the presence of
other MNPs (MnFe O , MnFe O @SiO , MnFe O @SiO -PrNH , MnFe O @
2
4
2
4
2
2
4
2
2
2
4
SiO -Pr-TDCl and MnFe O @SiO -Pr-BTEAT) as catalysts and the results are
2
2
2
4
2
shown in Table 1 (Entries 9–13). After optimizing the conditions, the synthesis
of spiroperimidine derivatives was carried out and high yields (73–94%) of the
desired products obtained (Scheme 2, Table 2). All the products were carefully
1
3

N. Ahadi et al.
Scheme 3 Synthetic pathway of spiropyranopyrazoles and pyranopyrazoles
characterized by possible comparison of physical constants, elemental analysis,
1
13
FT-IR, H-NMR and C-NMR spectroscopy (SI). In continuation, this work
was compared with other reported procedures for the synthesis of spiroperimi-
dine derivatives (Table 3). The results conꢂrm MNPs@SiO -BTEAT-SO H is a
2
3
suitable and eꢁcient catalyst in the synthesis of spiroperimidines with respect to
time and yield.
At the second step, the catalytic activity of MNPs@SiO -BTEAT-SO H was
2
3
studied in the model reaction of 4-chlorobenzaldehyde, malononitrile, ethyl ace-
toacetate and hydrazine hydrate to aꢀord the desired pyranopyrazole product
(
Table 4). The reaction was performed in the presence of varying amounts of cat-
alyst, various solvents and diꢀerent temperatures (Table 4). The results show the
best eꢁciency gained in the presence of 15 mg MNPs@SiO -BTEAT-SO H as
2
3
a catalyst and H O as solvent at room temperature (Table 4, Entry 4). Moreover,
2
the presence of a catalyst is necessary for reaction performance, and the cata-
lytic activity of MNPs@SiO -BTEAT-SO H is superior in comparison with other
2
3
catalysts (Table 4, Entries 2, 8–12).
After optimizing the reaction, various carbonyl compounds were used in the
reaction and the desired products were obtained in high yields within short times
1
3

Preparation and characterization of a novel organic–inorganic…
Table 1 Optimization for the synthesis of spiroperimidine derivatives in the presence of model reaction
NH NH
O
2
2
HN NH
+
a
Entry
Conditions/solvent
Catalyst
MNPs@SiO -BTEAT-SO H (10 mg)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
0
1
2
3
Reꢃux/H O
4
75
80
75
80
Trace
94
93
40
79
57
75
67
80
2
2
3
Reꢃux/EtOH
MNPs@SiO -BTEAT-SO H (10 mg)
1.45
2.30
2
24
1
1
7
1
1
2
3
Reꢃux/EtOH:H O (1:1)
MNPs@SiO -BTEAT-SO H (10 mg)
2
2 3
80 °C/Solvent-free
Reꢃux/EtOH
70 °C/EtOH
70 °C/EtOH
r.t/EtOH
70 °C/EtOH
70 °C/EtOH
70 °C/EtOH
70 °C/EtOH
70 °C/EtOH
MNPs@SiO -BTEAT-SO H (10 mg)
2 3
–
MNPs@SiO -BTEAT-SO H (20 mg)
2
3
MNPs@SiO -BTEAT-SO H (30 mg)
2
3
MNPs@SiO -BTEAT-SO H (20 mg)
2
3
MnFe O (20 mg)
2
4
1
1
1
1
MnFe O @SiO (20 mg)
2
4
2
MnFe O @SiO -PrNH (20 mg)
1
1
1
2
4
2
2
MnFe O @SiO -Pr-TDCl (20 mg)
2
4
2
2
MnFe O @SiO -BTEAT(20 mg)
2
4
2
aIsolated yield
Table 2 Synthesis of spiroperimidine derivatives in the presence of MNPs@SiO -BTEAT-SO H (20 mg)
2
3
nanoparticles as catalyst
Entry
Compounds
Product
Time (h)
Yield (%)a
mp (°C)
Obtained
Reported
1
2
3
4
5
6
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
1
3
1.5
1
2
94
73
85
87
80
92
109–110
85–88
171–172
240–241
230–233
282–283
110–111 [27]
84–86 [18]
171–173 [27]
242–244 [18]
236 [33]
2
>290 [33]
a
Isolated yield, reaction conditions: naphthalene-1,8-diamine (1, 1 mmol, 0.2 g), ketone (2a–b)/isatin
derivatives (2c–e)/1H-indeno[1,2-b] quinoxalin-11-one (2f, 1 mmol) and MNPs@SiO -BTEAT-SO H
2
3
(
20 mg) in the presence of 5 mL ethanol at 70 °C
(
Scheme 3, Table 5). Initially, various aromatic aldehydes were used as start-
ing carbonyl compounds and the equivalent products were produced in excel-
lent yields (Table 5, Entries 1–7). The presented results conꢂrm that the reac-
tions with aromatic aldehydes bearing electron-withdrawing substituents are
1
3

N. Ahadi et al.
Table 3 Comparison of MNPs@SiO -BTEAT-SO H catalyst with other reported catalysts in the synthe-
2
3
a
sis of spiroperimidine in model reaction
Entry
Condition
Catalyst
Time (min)
Yield (%)
References
1
2
3
4
H O: EtOH, 50 °C
EtOH, 75 °C
Solvent-free, 70 °C
EtOH, 70 °C
MNPs-TBSA
Phenylboronic acid
SA
120
30
75
70
92
81
94
[27]
[34]
[33]
This work
2
MNPs@SiO -BTEAT-SO H
60
2
3
aReagents: 1,8-diaminonaphtalene (1 mmol), cyclohexanone (1 mmol)
Table 4 Optimization of the reaction conditions for the synthesis of pyranopyrazole derivatives in the
presence of model reaction
H N
2
CHO
Cl
O
NC
CN
CN
O
O
NH
N
+
+
+ NH -NH .H O
2 2 2
OEt
Cl
Entry
Conditions/solvent
Catalyst (mg)
MNPs@SiO -BTEAT-SO H (10 mg)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
1
1
1
r.t/H O
30
420
15
15
35
30
25
30
45
40
50
35
87
25
95
93
75
75
83
77
65
73
67
73
2
2
3
r.t/H O
–
2
r.t/H O
MNPs@SiO -BTEAT-SO H (15 mg)
2
2 3
r.t/H O
MNPs@SiO -BTEAT-SO H (30 mg)
2 3
2
r.t/EtOH
MNPs@SiO -BTEAT-SO H (15 mg)
2 3
r.t/EtOH:H O (1:1)
MNPs@SiO -BTEAT-SO H (15 mg)
2 3
2
H O/reꢃux
MNPs@SiO -BTEAT-SO H (15 mg)
2
2
3
r.t/H O
MnFe O (15 mg)
2
2
4
r.t/H O
MnFe O @SiO (15 mg)
2
2 4 2
0
1
2
r.t/H O
MnFe O @SiO -PrNH (15 mg)
2 4 2 2
2
r.t/H O
MnFe O @SiO -Pr-TDCl (15 mg)
2
2 4 2 2
r.t/H O
MnFe O @SiO -NH-BTEAT (15 mg)
2 4 2
2
aIsolated yield
performed in shorter times than aldehydes including electron-donating substitu-
ents. At the second step, various ketones including indoline-2,3-dione derivatives,
1
H-indene-1,2,3-trione and 11H-indeno[1,2-b]quinoxalin-11-one were inserted
in the designed reaction and the desired valuable spiroproducts were acquired in
good yields (Table 5, Entries 8–17). To the best of our knowledge, the product
1
1g, 13a and 14 are synthesized for the ꢂrst time. All the products were carefully
characterized by possible comparison of physical constants, elemental analysis,
1
3

Preparation and characterization of a novel organic–inorganic…
Table 5 Synthesis of pyranopyrazole and spiropyranopyrazole derivatives in the presence of MNPs@
SiO -BTEAT-SO H as a catalyst
2
3
Entry Ar or carbonyl com-
pound
R4 R3
Product Time (min) Yield (%) Mp (°C)
Obtained Reported
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
4-Cl–C H
H
H
H
H
H
CN
11a
11b
11c
11d
11e
11f
11g
12a
12b
12c
15
20
30
25
45
115
35
100
80
110
140
125
145
100
200
130
180
95
92
87
80
80
81
95
95
93
85
80
85
78
83
80
82
81
230–232 226–228 [35]
231–232 229–230 [36]
206–208 210–212 [37]
200–202 208–209 [38]
180–181 183–185 [39]
218–220 203–205 [40]
6
4
2,4-(Cl) –C H
CN
CN
CN
CN
2
6
3
4-OMe–C H
6
4
4-Me–C H
6
4
4-Br–C H
6
4
4-Cl–C H
Ph CN
6
4
3-NO –4-OH–C H
H
H
H
H
H
H
H
H
CN
CN
CN
CN
223
–
2
6
3
8a
8b
8c
8a
8b
8c
9
10
8a
9
285–287 278–280 [25]
255–257 268–270 [25]
280–283 281 [25]
280–281 280–282 [25]
127–130 126–127 [41]
255–256 250–254 [39]
0
1
2
3
4
5
6
7
CO Et 12d
2
CO Et 12e
2
CO Et 12f
2
CN
13a
14
12g
13b
291–292
248–249
−
−
Ph CN
Ph CN
Ph CN
225–226 227–229 [41]
219–220 220–222 [40]
a
Isolated yield, Reaction conditions: aryl aldehydes (1 mmol) or ketones (1 mmol), hydrazine hydrate
1.5 mmol), ethyl acetoacetate (1 mmol), malononitrile (1 mmol) and MNPs@SiO -BTEAT-SO H
(
(
2
3
15 mg) in the presence of 10 mL water at room temperature
Table 6 Comparison of MNPs@SiO -BTEAT-SO H catalyst with other catalysts reported for the syn-
2
3
a
thesis of spiropyranopyrazoles in the model reaction
Entry Condition
Catalyst
Time (min) Yield (%) References
1
2
3
4
5
6
H O, 80 °C
Solvent-free, 90 °C
Solvent-free, 100 °C
Nano-SiO2
[DMBSI]HSO4
Nano[Fe-PSMP]Cl2
Aspirin
Meglumine
35
18
5
30
15
90
88
85
92
95
97
[37]
[42]
[43]
[39]
[36]
[29]
2
EtOH:H O, 60 °C
2
H O, r.t
2
H O, r.t
(NiFe O @SiO -Preyssler) NFS- 15
2
2 4 2
PRS
7
8
9
H O:EtOH (9:1), 80 °C β-Cyclodextrin
15
4
15
92
94
95
[44]
[35]
This work
2
Solvent-free, 100 °C
[cmpy]I
H O, r.t
MNPs@SiO -BTEAT-SO H
2
2
3
a
Reagents: malononitrile (1 mmol), hydrazinhydrate (1 mmol), 4-chlorobenzaldehyde (1 mmol), ethyl-
acetoacetate (1 mmol)
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3

N. Ahadi et al.
1
13
FT-IR, H-NMR and C-NMR spectroscopy (SI). The comparison of MNPs@
SiO -BTEAT-SO H catalyst with other reported catalysts in the model reaction
2
3
is provided in Table 6. The MNPs@SiO -BTEAT-SO H displays good or higher
2
3
performance in comparison with other catalysts.
Reusability of recyclability the MNPs@SiO ‑BTEAT‑SO H catalyst
2
3
In the green synthetic processes, the reusability and recyclability of catalysts are
essential. Therefore, the reusability of MNPs@SiO -BTEAT-SO H was evalu-
2
3
ated in the model reactions. After completion, the solvent was evaporated, the
precipitate was dissolved in ethanol and the catalyst was separated by a magnet.
The recovered catalyst was reused in the ensuing reaction without further acti-
vation. As shown in Fig. 7a, the catalyst could be recycled without any change
in catalytic activity in ꢂve runs. The FT-IR spectra (Fig. 7b) and XRD patterns
(
Fig. 7c) of fresh and reused catalysts are compared. The reused catalyst receives
no noticeable change in structure. Also, Fig. 7d indicates an easy separation of
the hybrid catalyst by an external magnet (a) and re-dispersion of MNPs@SiO -
2
BTEAT-SO H after removal of the magnet (b). These results conꢂrm that the
3
MNPs@SiO -BTEAT-SO H has excellent stability and performance in organic
2
3
reactions.
Fig. 7 Recyclability of MNPs@SiO -BTEAT-SO H (a), FT-IR spectra (b) and XRD patterns (c) of the
2
3
reused and fresh catalyst, magnetic separation and re-dispersion of catalyst (d)
1
3

Preparation and characterization of a novel organic–inorganic…
Plausible mechanism for the synthesis of products in the presence of MNPs@
SiO ‑BTEAT‑SO H as a catalyst
2
3
A plausible pathway for the synthesis of spiroperimidine derivatives in the pres-
ence of the MNPs@SiO -BTEAT-SO H catalyst is shown in Scheme 4. Initially,
2
3
the carbonyl group is typically activated by MNPs@SiO -BTEAT-SO H catalyst,
2
3
and a nucleophilic attack of the 1,8-diaminonaphthalene on the activated carbonyl
group produces intermediate A. The imine bond attacked by NH , and intermediate
2
+
B performed. At last, the possible removal of H aꢀorded the desired spiroperimi-
dine [27].
A proposed mechanism for the synthesis of pyranopyrazole derivatives in the
presence of MNPs@SiO -BTEAT-SO H is described in Scheme 5. Initially, a
2
3
condensation of hydrazine hydrate and ethyl acetoacetate produces the 3-methyl-
1
H-pyrazol-5-ol (intermediate A). The Knoevenagel condensation between malo-
nonitrile and activated carbonyl compound produced the arylidenemalononitrile
(
intermediate B). Subsequently, the Michael addition takes place between intermedi-
ate A and intermediate B and the successive tautomerization resulted in the pyrano-
pyrazole formation [25, 45]. For consolidation, the intermediates A and B were syn-
thesized and identiꢂed (SI). The typical reaction of as-prepared intermediates A and
B successfully produced the desired product.
Scheme 4 Plausible mechanism for the synthesis of spiroperimidines
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3

N. Ahadi et al.
Scheme 5 The plausible mechanism for the synthesis of pyranopyrazoles
Conclusion
A new hybrid inorganic–organic nanocatalyst (MNPs@SiO -BTEAT-SO H) as a
2
3
recyclable and highly eꢁcient heterogeneous catalyst was prepared. The FT-IR,
XRD, VSM, EDS, EDS map and SEM analysis techniques have been conꢂrmed
the successful preparation of hybrid nanostructure and its excellent stability. The
application of MNPs@SiO -BTEAT-SO H in the organic synthesis conꢂrms its
2
3
eꢁciency as a suitable heterogeneous catalyst in the synthesis of spiroperimi-
dines, pyranopyrazole and spiropyranopyrazole derivatives. The MNPs@SiO -
2
BTEAT-SO H has high acidity. In addition, we think that the long organic tags
3
grafting and triazine ring moiety resulted in an intense performance of MNPs@
SiO -BTEAT-SO H in organic solvents and aqueous medium. The advantages
2
3
of this work are high yields, short reaction times, use of a green solvent, easy
workup procedure, catalyst reusability without signiꢂcant diminishing in its
eꢁciency and simple separation of hybrid nanocatalyst by applying an external
magnet.
Acknowledgements This study was supported by the Research Council of Arak University (Grant No.
9
4Ah.Ph.D).
Compliance with ethical standards
Conꢁict of interest The authors have no other conꢃict of interest to declare.
1
3

Preparation and characterization of a novel organic–inorganic…
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